Proline dehydrogenase from Thermus thermophilus does not discriminate between FAD and FMN as cofactor

Sci Rep. 2017 Mar 3;7:43880. doi: 10.1038/srep43880.

Abstract

Flavoenzymes are versatile biocatalysts containing either FAD or FMN as cofactor. FAD often binds to a Rossmann fold, while FMN prefers a TIM-barrel or flavodoxin-like fold. Proline dehydrogenase is denoted as an exception: it possesses a TIM barrel-like fold while binding FAD. Using a riboflavin auxotrophic Escherichia coli strain and maltose-binding protein as solubility tag, we produced the apoprotein of Thermus thermophilus ProDH (MBP-TtProDH). Remarkably, reconstitution with FAD or FMN revealed that MBP-TtProDH has no preference for either of the two prosthetic groups. Kinetic parameters of both holo forms are similar, as are the dissociation constants for FAD and FMN release. Furthermore, we show that the holo form of MBP-TtProDH, as produced in E. coli TOP10 cells, contains about three times more FMN than FAD. In line with this flavin content, the crystal structure of TtProDH variant ΔABC, which lacks helices αA, αB and αC, shows no electron density for an AMP moiety of the cofactor. To the best of our knowledge, this is the first example of a flavoenzyme that does not discriminate between FAD and FMN as cofactor. Therefore, classification of TtProDH as an FAD-binding enzyme should be reconsidered.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Bacterial Proteins / chemistry
  • Bacterial Proteins / genetics
  • Bacterial Proteins / metabolism*
  • Crystallography, X-Ray
  • Escherichia coli / genetics
  • Escherichia coli / metabolism
  • Flavin Mononucleotide / chemistry
  • Flavin Mononucleotide / metabolism*
  • Flavin-Adenine Dinucleotide / chemistry
  • Flavin-Adenine Dinucleotide / metabolism*
  • Holoenzymes / chemistry
  • Holoenzymes / metabolism
  • Kinetics
  • Maltose-Binding Proteins / metabolism
  • Models, Molecular
  • Molecular Structure
  • Proline Oxidase / chemistry
  • Proline Oxidase / genetics
  • Proline Oxidase / metabolism*
  • Protein Conformation
  • Recombinant Proteins / chemistry
  • Recombinant Proteins / metabolism
  • Thermus thermophilus / enzymology*
  • Thermus thermophilus / genetics

Substances

  • Bacterial Proteins
  • Holoenzymes
  • Maltose-Binding Proteins
  • Recombinant Proteins
  • Flavin-Adenine Dinucleotide
  • Flavin Mononucleotide
  • Proline Oxidase